| Summary: | This study investigated the flexural behavior of composite beams with ultra-high performance concrete (UHPC) T-section and hot rolled steel (HRS) H-section. First, a four-point bending test on six specimens was conducted. The effects of stud spacing and tensile reinforcement ratio on flexural performance were investigated in terms of crack patterns, failure modes, ultimate load, load-strain response, relative interfacial slip, and ductility. The experimental results indicated that the stud spacing and the presence of tensile reinforcement had a visible effect on the crack patterns of UHPC web. The distribution of group cracks was observed at UHPC web of specimens with unreinforced UHPC bulb. During the failure stage, the whole HRS H-section in the constant moment region yielded. In particular, the partial cross section of HRS entered the strain hardening stage. In addition, an analytical approach verified by six tested specimens was developed to study the moment-curvature response of HRS-UHPC composite beams (HUCBs). The comparison results indicated the good accuracy of the analytical approach. Then, the proposed sectional analysis model was utilized to investigate the effects of the strength of HRS and UHPC, the total depth of cross section, and the depth of HRS H-section on yielding moment, including ultimate moment and ductility. The analytical results revealed that the strength of HRS and the total depth of cross section had a significant impact on the moment-curvature response of HUCBs. The sectional analysis also illustrated that the yielding point was mainly determined by the yielding of HRS H-beam. Compared with UC120, the ultimate moment and ductility coefficient of the composite beam using UC200 increased by 20.6 % and 87.7 %, respectively. However, the tensile strength of UHPC had a slight influence on the yielding and ultimate moment as well as ductility.
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